Our technique of electrophoretic determination of lactate dehydrogenase (LD) isoenzymes has been improved by: 1) clear separation and demonstration of the isoenzymes on agarose gel covered slides which allowed accurate quantitation, 2) use of the same method to obtain normal patterns in tissues and blood cells, as well as reference values in serum for meaningful comparisons and correlations of results, and 3) estimation of the ratio of the cardiac associated LD-isoenzymes-1 and 2. The improved technique enhanced diagnostic discrimination of myocardial infarction and other complications in patients undergoing cardiac operations.